Communication system



April 1944- R. H. CAMPBELL COMMUNICATION SYSTEM Filed Dec. 14, 1942 2 Sheets- Sheet l April 18, 1944. R, H. CAMPBELL COMMUNICATION SYSTEM 2 Sheets-Sheet 2 Filed Dec. 14, 1942 Patented Apr. 18, 1944 UNITED STATES PATENT OFFICE COMMUNICATION SYSTEM Richard H. Campbell, Racine, Wis., asslgnor to Webster Electric Company, Racine, Win, a corporation of Delaware Application December 14, 1942, Serial No. 468,882

19 Claims.

The present invention relates to lntercommunicating systems and particularly to the prouision of new and improved circuit arrangements enabling an operator at one station to indicate to an operator at another station that he is desirous of interrupting or breaking in on the Other obJects and advantages of the present operator at the other station when the latter is invention will become appare o the e sui talking to the former. description, in the course of which reference In intercommunlcating systems, and particuis had to the accomp nyi drawings, n which! larly in intercommunicating systems of the loud Fig. 1 is a schematic representation of an inspeaker type, there has been developed a type of tercommunicating system embodying the present system wherein a talk-listen switch is utilized invention; and alternately to condition a station for transmis- Fig. 2 is a similar representation of a modified sion or reception. In some systems alternate system. operation of switches at two stations between In the embodiment of the invention illustrated their talk and listen positions is required in in Fi 1. there is s own an intercommunication order for communication to be carried on bey tem Of t e 1 p a typ w r n 0 tween the two stations. In other systems the uni ation can be a d on a t r t y in 0D- direction of communication is controlled by the posite directions between a plurality of master operation of a switch at one station between its stations under the control of communication two positions. In systems of both these types direction control switches, and wherein comit may happen that an operator at a station conmunication may be carried on between a master ditioned for reception desires to interrupt transstation and substations under the control of a mission by the station conditioned for transcommunication direction control switch at the mission, and it is one of the primary objects of master station. the present invention to provide arrangements The master stations illustrated in Fig. 1 are whereby a station conditioned for reception may indicated by reference characters I, 2, and 3, and signal a station conditioned for transmission a single substation by reference character 4. that it is desired to interrupt or break in on the These stations are provided with translating delatter. In my co-pending application, applicavices capable of being utilized both as microtion Serial No. 457,549, filed September 7, 1942, phones and loudspeakers, such as the loudspeakthere are illustrated systems embodying this ers II to l4, inclusive, which may be of the break in" feature. The systems illustrated in well-known permanent magnet type. The masthe aforesaid application are of a type wherein ter stations are provided with amplifiers I5, l6, communication is carried on in one direction and I1, communication direction control switches over one circuit and in the opposite direction 2 and 23, and banks of station selector over another circuit. The present application, switches 24, 25, and 26, all respectively. however, is directed more particularly to sys- The amplifiers may be of any well-known contems wherein communication is carried on alterstruction, and they have, therefore, not been 11- nately in opposite directions over a single cir- 4o lustrated in detail. It is deemed suflicient to cuit. state that each amplifier is provided with an in- It is, therefore, a more specific object of the put transformer 21 and an output transformer present invention to provide systems wherein 28, and that the amplifiers are each connected to communication is alternately carried on in opa chassis and a common ground by a conductor posite directions over a single circuit with a sig- 29. Power is supplied to each amplifier through nalling arrangement whereby a station condian associated rectifier 30, which may be of contioned for transmission can be signalled that anventional construction including a single rectifier other station desires to interrupt the transmistube 3| (illustrated in detail only at station I) sion therefrom. connected for full wave rectification. The am- Another object of the present invention is to plifier, while connected to the rectifier, is not provide a system comprising one or more massupplied with plate potential except when the ter stations, 1. e., stations provided with an amcommunication direction control switch is in its plifier and a communication direction control talk or listen position. In the idle posiswitch, and one or more substations, i. e., station, in which the various communication directions having no amplifier, with signalling 'artion control switches are illustrated, the supply rangements whereby a substation can signal a master station that it is desired to interrupt transmission from the master station when the latter is conditioned for transmission and the substation for reception.

of plate potential is interrupted by a switch blade 32, referring now more particularly to the equipment at station I, forming a part of communication direction control switch 2I. In the two other positions of the communication direction control switch (the talk" and listen positions), the switch blade 32 is adapted to complete the plate voltage supply circuit from the rectifier to the amplifier through conductor 33 and a filter 34, also of conventional construction.

The amplifiers are all conditioned to be ready for instantaneous use whenever a communication direction control switch is operated to condition the station for talking or listening. Such operation of the switch completes the plate sup ply circuit as previously described. Since it is contemplated that the various tubes of the amplifiers are continuously supplied with heating current from a transformer 35, it will be noted that the completion of the plate voltage supply circuit will immediately render the amplifiers operative. I

The communication direction control switch 2I is a multipole three-position switch. In a first position (the up and idle position) the loudspeaker II is connected directly to a communication circuit 40 for the reception of calls from other stations provided with amplifiers, that is, from other master stations. In a second position (the intermediate and listening position), the loudspeaker is connected to the output, and the communication circuit to the input of the amplifier. In a third position (the down and talking position, from which the switch is biased by a spring 4i into its intermediate position upon release), the loudspeaker is connected to the input, and the communication circuit to the output of the amplifier.

The connection of the loudspeaker to the communication circuit in the idle position of the communication direction control switch is as follows: The pair of switch blades 42, and a two-conductor circuit 43 are connected to the voice coil of loudspeaker II.

The connections of the loudspeaker to the amplifier output and the communication circuit of the amplifier input in the intermediate position of switch 2I are as follows: The loudspeaker II is connected to the output of the amplifier through circuit 43, the pairs of switch blades 44, and circuit 45. At the same time, resistor 46 is connected in parallel with the loudspeaker by switch blade 46', and resistor 41 is connected in series with the loudspeaker. Resistor 41 serves to decrease the reception volume, whereas resistor 46 serves to maintain constant the impedance of the loudspeaker circuit. The communication circuit 40 is connected to the amplifier input through the switch blades 42 and circuit 48.

The connections of the loudspeaker to the input and the communication circuit to the output'of the amplifier in the third position of switch 2| are as follows: The loudspeaker is connected to the input of the amplifier through circuit 43, the switch blades 44 and circuit 48. Communication circuit 40 is connected to the amplifier output through switch blades 42 and circuit 45.

The station selector switch 24 includes a plurality of switches 52, 53, and 54 for connecting the communication circuit 40 to selected ones of interstation circuits 55, 50, 51, and 58 which are individual to stations I, 2, 3, and 4, respectively. Under normal conditions, the selector switch 5|, which is individual to station I, is

closed in order that other stations equipped with amplifiers may call station I.

Inasmuch as the circuits and switches at stations 2 and 3, corresponding to those already described at station I, are identical, it is deemed unnecessary to describe these in detail. However, corresponding elements and circuits have been indicated at stations 2 and 3 by using the same reference characters and adding thereto the suffixes 2 and 3 respectively. It should be noted though, that at station 2 the selector switch 52-2 individual to station 2 is normally closed, whereas at station 3 the selector switch 53-3 individual to station 3 is normally closed.

The loudspeaker I4 at station 4 is connected by a circuit including two conductors 50 directly to interstation circuit 58 individual to station 4.

The present invention is, as has already been indicated, directed to the feature of providing signalling means for indicating at a station conditioned for transmission that it is desired to interrupt the transmission from that station. In the system of Fig. 1 the master stations are, therefore, provided with signal lights BI, 6I-2, and Ill-3 so arranged in circuit that they can be controlled to indicate a desire to interrupt or break in on transmission from a station conditioned for transmission from one conditioned for reception.

In the following description of the signalling arrangement the apparatus at station I alone will be described and similar reference characters, together with suifixes of the character previously used will be used to indicate corresponding apparatus at stations 2 and 3. The signal light 6|, which is preferably a neon lamp (such as the type NE-I l manufactured by the General Electric Company) is connected to the amplifier side of the plate voltage circuit through conductor 62 and resistor 83. The other terminal of the lamp is connected to the common ground through resistor 64. The ungrounded terminal of the lamp is also connected by a conductor 55 to the junction of a pair of resistors 66, connected across the communication circuit. A second pair of resistors 61 is connected across the circuit 43 (and is thus in parallel of the voice coil of the loudspeaker), and their junction is connected by conductor 68 to the common ground. The resistors may have values about as follows: the resistor 63about 50,000 ohms, the resistor ISL-200,000

ohms, and resistors 66 and 61 a value of about 500 ohms each.

The circuit at station 4 also includes a pair of resistors 69 connected across circuit 59. These may have a value equal to the values of resistors 66 and 61, Their junction point is connected to a common ground through a conductor 1.0 and a switch 'II normally closing the ground circuit, but operable against the bias of a spring I2 to open the circuit to signal a desire to break in, as will be described hereinafter.

In the operation of the system described in detail it is contemplated that each of the amplifiers will normally be supplied with power from a suitable alternating current source connected to the rectifiers associated therewith. The communication direction control switches at the various stations will normally be in their idle positions, and the station selector switches individual to the reception stations are closed to condition them for reception for calls from other stations.

Under normal conditions, the neon lamps 6| are de-energized because no power is supplied to them-the various plate supply circuits being broken by the communication direction control switch blades 32. Assuming now that the operator-at station I desires to call the pperator at station 2, the operator at station I first closes station selector switch 52 connecting circuit 40 to interstation circuit 56, to which the loudspeaker I2 is i normally connected through station selector switch 52--2 at station 2. The operator at station I then operates the communication direction control switch 2| to its lowermost, or talk" position. Upon-so doing, the loudspeaker II is connected to the amplifier input, and the amplifier output is connected to circuit 40 as heretofore described in detail. As a result, the operator at station I can transmit to station 2.

Whenstation I is transmitting to'station 2 as described immediately above, the signal lights at stations I and 2 are both unlit, even though the plate supply circuit at station I is completed. At this ,time the ungrounded' terminals of both the neon lamps are connected to the plate supply at station I, but both lamps are grounded and consequently they do not light, the two lamps SI and BI-2 being grounded through the common ground 29 at station 2. The lamp 6| at station I is grounded through a circuit including conductor 65, resistors 66, circuit 40, switch 52, circuit 56, switch 522, circuit 402, switch blades 42-2 in their uppermost positions, circuit 43-2, resistors 612, and circuits 682 and 29.

After thus selecting and calling station 2, the operator at station I controls the direction of communication by operating-the switch 2| between its middle and lowermost position. During such operation the two lamps 6| remain unlit by reason of their being connected to ground as heretofore described.

When station I is transmitting to station 2, the operator at station 2 may signal the operator at station I that it is desired to break in on the transmission from that station. This can be done simply by opening and closing the selector switch 52-2, with the result that the previously described ground circuit for the lamp 6| at station I is periodically broken, and the lamp 6| is thus periodically lit. Upon observance of the lighting of lamp 6!, the operator at station I can operate switch 2| to its listen position to enable the operator at station 2 to transmit to station I.

In the event station 2 calls station I, the operation is identical with that described above, ex cept that the operator at station 2 initiates the call and controls the direction of communication. In similar manner station 3 may call either station 2 or station I, or either of the two last mentioned stations can call station 3.

In the event communication is carried on between one of the master stations and substation 4 then, when the former is transmitting, the operator at the latter can signal a desire to break in on the transmission. Assuming now that the operator at station I desires to communicate with station 4, the operator at station I closes selector switch 54 and operates the communication direction control switch 2I to its lowermost position. When this is done, loudspeaker II is connected to the input of the amplifier and loudspeaker I4 to the output of the amplifier. The direction of communication is controlled by the operator at station I in the same manner as when station I calls station 2. When station I is conditioned for transmission, by operation of the communication direction control switch 2| to its lowermost or talk position (or for that matter in its intermediate, or listening, position) the lamp 6| is connected to the plate supply voltage. It is, however, prevented from being lit by the ground circuit extending through the switch II at station 4. Thus, when the switch 'II is opened by the operator at station 4, the ground is removed with the result the lamp 6| is lit to give an indication of a desire to break in on the transmission from station I.

In the embodiment of the system illustrated in Fig. 2 the break-in signalling arrangement is applied to a somewhat difi'erent type of intercommunicating system consisting solely of master stations. In this system the master stations are provided with two-position communication direction control switches, and these are so arranged that when two stations are in communication, the switches at these two stations are alternately operable between their positions alternately to condition one or the other station for transmission to the other over a single interstation circuit. In one direction of transmission or communication the amplifier at one station is used, whereas in the other direction of transmission the amplifier at the other station is used, the amplifier at the station conditioned for transmission being used in each case.

The break-in signalling arrangement embodied in the system of Fig. 2 is so constructed and arranged that the signal lights at the master stations are unlit when either one or both stations are conditioned for reception and both are lit when both stations are conditioned for transmission. Thus, a station normally receiving from another may indicate a desire to break in upon the other by operating the communication direction control switch to its talk position.

The system illustrated in Fig. 2 is similar in many respects to that illustrated in Fig. 1, except primarily for the construction of the communication direction control switches, and arrangement of circuits controlled thereby and, in order to simplify the description, the corresponding elements in the two systems have been indicated by like reference characters, and in the following description emphasis is placed on the differences between the two systems.

The communication direction control switch 2| at station I is of the two-position type. In its indicated position the switch conditions the station for reception from other stations, and in its other position it conditions the station for transmission through the amplifier I5 at station I.

In the indicated normal position of the switch the loudspeaker II is connected to communication circuit 40, through circuit 43, a pair of switch blades IOI, the lowermost one of which is directly connected to the lower conductor 40 and the upper one of which is connected to the upper conductor 40 through conductor I02, potentiometer I03 and switch blade I04. Thus, the reception volume may be controlled by the potentiometer I03. In the normal position of the switch, the plate supply voltage is disconnected from the amplifier by the switch blade 32, forming part of, and operable simultaneously with the, communication direction control switch.

In the talk position of the switch 2|, loudspeaker II is connected to the input of the amplifier I5 and the output of the amplifier is connected to communication circuit 40. The loudspeaker II is connected to the amplifier input through circuit 43, switch blades IN, and circuit 48. The output of the amplifier is connected to circuit 40 through circuit 45 and switch blades IM and I05. In this position of switch 2I the amplifier is supplied with plate voltage and the potentiometer is disconnected so that the full amplifier output is utilized for transmission. The switch blade I05 also serves to short circuit the amplifier output when the communication direction control switch is in its normal position.

The apparatus at stations 2 and 3 corresponds identically with that at station I, and corresponding elements have been indicated by the references used in describing the apparatus at station I with the suflixes -2 and -3.

Under normal conditions, that is, when the system is in a quiescent state, and the various communication direction control switches are in their indicated listen positions, the break-in signal lamps are all de-energized. This results from the disconnection of the plate supply voltages from the amplifiers and from the lamps by the switch blades 32 of the communication direction control switches.

When stations I and 2 are in communication with each other, then the station conditioned for reception can indicate a desire to break in on the station conditioned for transmission by operation of the communication direction control switch thereat to its talk position. Assuming now that station I desires to communicate with station 2, the operator at the former operates the station selector switch 24 to connect circuits 40 and 56, the latter being individual to station 2. Then, the operator at station I operates switch H to condition the station for transmission. When this is done, loudspeaker II is connected to the input of amplifier I5, and the output of the amplifier is supplied to loudspeaker I2 at station 2 through circuit 40, selector switch 24, interstation circuit 56, selector switch 25 (which is normally in circuit closing relationship to interstation circuit 56), circuit 40--2, potentiometer I03--2, switch blades IIII2, and circuit 43-2. When the operator at station I is through talking, he simply releases switch 2I, which is then returned by spring 4| to its listen position, and the operator at station 2 operates switch 22 to its talk position with the result that loudspeaker I2 is connected to the input of amplifier I6, and the output of the latter is connected to loudspeaker II at station I through a circuit including the interstation circuit 56.

If the operator at station I wants to indicate a desire to break in on the operator at station 2, it is necessary only that switch 2| at station I be operated to its talk position. If this be done, then both signal lights GI and 6I-2 are lit. In the embodiment of Fig. 2, as in the embodiment of Fig. l, the signal lamps are supplied with voltage only when the communication direction control switches are in their talk positions. Furthermore, the lamps are grounded when either of the stations is conditioned for reception, the ground extending through the resistors 66 and B1, and the ground conductor 68 at one or other of the stations-normally the station conditioned for reception. When the station conditioned for reception also operates the communication direction control switch thereat to its talk position, then the ground circuit is removed and both lamps are lighted. Prior to operation of switch 2| to its talk position, both lamps GI and 6I-2 were supplied with power from the plate supply at station 2, but both were grounded through conductor 68 at station I by reason of the switch blades IIII connecting circuits 40 and 43. However, when switch 2I is operated to its talk position, circuit 40 is disconnected from the ground circuit 68, and the lamps are energized as a result of this disconnection from the ground.

The above described mode of operation is followed with similar results in case either of stations I or 2 communicates with station 3.

In both the embodiments of Figs. 1 and 2, the signal circuits are balanced relative to the communication circuits as the signal circuits are connected to the junction points of equal value resistors connected across the communication circuits. This arrangement enables the communication circuits to be used also as signal circuits.

While both of the embodiments of the invention hereinabove described comprise a limited number of master stations and a single substation, it should be understood that the systems may comprise a larger number of stations of either type, and that other modifications may be made in the particular circuit arrangements without departing from the principles of the invention.

Having thus described my invention, what I claim as new and desire to secure by Letter Patent of the United States is:

1. In an intercommunicating system of the type comprising a station having a communication direction control switch operable alternately to condition the station for reception or transmission over a single circuit and a second station adapted to be connected to the first over said single circuit, the combination including, signal means at the first station, and means including signal means control circuits and a switch at the second station controlling said circuits so constructed and arranged that the signal means at the first station can be operated from the station when the first is conditioned for transmission and the second for reception for providing a signal at the station conditioned for transmission that it is desired to break in on the transmission from the station.

2. In an intercommunicating system of the type comprising a first station having a communication direction control switch operable alternately to condition the station for reception or transmission over a single circuit and a second station adapted to be connected to the first over said single circuit, the combination including, signal means at the first station, and means including a switch at the second station for operating said signal means when the communication direction contrcl switch at the first station conditions that station for transmission, thereby to indicate a desire to break in on the transmission from the first station.

3. In an intercommunicating system of the type comprising a first station having a communication direction control switch operable alternately to condition the station for reception or transmission, a second station and a single communication circuit between the stations over which communication can be carried on alternately in opposite directions under the control of said communication direction control switch, the combination including, signal means at the first station, and means including said communication circuit and a switch at the second station for operating said signal means when the communication direction control switch at the first station conditions that station for transmission, thereby to indicate a desire to break in on the transmission from the first station.

4. In an intercommunicating system of the type including a first station having a communication direction control switch operable alternately to condition the station for reception or transmission over a single circuit and a second station adapted to be connected to the first over said single circuit, the combination including, signal means at said first station. signal controlling means at said first station for conditioning said signal means for operation when said communication direction control switch conditions said station for transmission, and means including signal controlling means at the second station for operating said signal means when said first station is conditioned for transmission.

5. In an intercommunicating system of the type including a first station having a communication direction control switch operable alternately to condition the station for reception or transmission over a single circuit and a second station adapted to be connected to the first over said single circuit, the combination including, signal means at said first station, switch means at said first station operable simultaneously with said communication direction control switch for conditioning said signal means for operation when said communication direction control switch is operated to condition said station for transmission, and means including switch means at the second station for operating said signal means when said first station is conditioned for transmission.

6. In an intercommunicating system of the type including a first station having a communication direction control switch operable alternately to condition the station for reception or transmission over a single circuit and a second station adapted to be connected to the first over said single circuit, the combination including, a signal light at said first station, a source of power for said light, ground circuits deenergizing the light at both stations, switch means at said first station operable simultaneously with said communication direction control switch for completing the connection of said light to said source of power and removing one of the said ground circuits when said communication direction control switch is operated to condition said station for transmission, and means including switch means at the second station for removing the other ground circuit when said first station is conditioned for transmission.

7. In an intercommunicating system of the type comprising a pair of stations each having a communication direction control switch operable to condition the station for reception or transmission over a single circuit, the combination including, signal means at each station, and means including control circuits and circuit controlling means at each station for operating the signal means at another when the communication direction control switch at said other station conditions said other station for transmission, thereby to indicate a desire to break in on the transmission from said other station.

8. In an intercommunicating system of the type comprising a pair of stations each having a communication direction control switch operable to condition the station for reception or transmission over a single circuit,-the combination including, signal means at each station, signal controlling means at each station for conditioning the signal means at that station for operation when the communication control switch thereat conditions the station for transmission, and signal controlling means at each station operable when the station is conditioned for transmission for operating the signal means at the other station when the signal means at the other station .is-

conditioned for operation.

9. In an intercommunicating system of the type comprising a pair of stations having communication direction control switches alternately operable to condition the stations for reception or transmission over a single circuit, the combination including, signal means at each station, and means including signal means control circuits and switch means operable simultaneously with the communication direction control switches controlling said circuits so constructed and arranged that the signal means at a station conditioned for transmission can be operated from a station conditioned for reception upon operation of the communication direction control switch at the latter station to condition it for transmission for providing a signal that it is desired to break in on the transmission from the station.

10. In an intercommunicating-system of the type comprising a pair of stations having communicating direction control switches alternately operable between talk and listen positions for providing two way communication between the stations over a single circuit, the combination including, a signal light at each station, a source of power at each station, and signal controlling means at each station operable simultaneously with the communication control switch thereat so constructed and arranged that the light at a station conditioned for transmission is energized when the communication direction control switch at the other station is operated to condition the other station for transmission.

11. In an intercommunicating system of the type comprising a Pair of stations having communication direction control switches alternately operable between talk and listen positions for providing two way communication between the stations over a single circuit, the combination including, signal means at each station connected to said communication circuit in balanced manner, and signal controlling means at each station including a ground connection adapted to be connected in balanced manner to said communication circuit and switch means associated with the communication control switch thereat so constructed and arranged that the signal means at a station conditioned for transmission is operated through said communication circuit when the communication direction control switch at theother station is operated to condition the other station for transmission.

12. In an intercommunicating system of the type comprising two or more stations adapted to be connected by a single interstation circuit each having an amplifier, a loudspeaker utilizable both as a receiver and a transmitter, station selector means, and acommunication direction control switch operable in one position to condition the station for reception over said interstation circuit by connection of the loudspeaker thereto through said selector means or for transmission over said interstation circuit by connection of the loudspeaker to the input of the amplifier and of the output to said circuit through the station selector means, whereby two way communication can be carried on between two stations by alternate operation of the switches thereat, including in combination, a signal light at each station, a source of power at each station, switch means operable with the communication direction control switch at each station, and circuits controlled thereby for short circuiting the light at the station'by connection thereof to a circuit common to the stations when the switches condition the stations for reception and for connecting the lights to the sources of power thereat and disconnecting them from said common circuit when the communication direction control switches condition the stations for transmission, whereby when the communication direction control switches at either or both of two stations connected to an interstation circuit connect the stations for reception, both lights are grounded and when both connect the stations for transmission, both lights are ungrounded and lit.

13. In an intercommunicating system of the type comprising two or more stations adapted to be connected by a single interstation circuit and a common ground connection and each having an amplifier, a loudspeaker utilizable both as a receiver and a transmitter, station selector means, and a communication direction control switch operable in one position to condition the station for reception over said interstation circuit by connection of the loudspeaker thereto through said selector means or for transmission over said interstation circuit by connection of the loudspeaker to the input of the amplifier and of the amplifier output to said circuit through the station selector means, whereby two way communication can be carried on between two stations by alternate operation of the switches thereat, including in combination, a pair of resistors at each station connected across said circuit at a point intermediate the selector means and communication direction control switch, a signal light at each station having one terminal connected to the junction of said resistors and its other terminal connected to said common ground, a source of power at each station, switch means operable with the communication direction control switch at each station for connecting the light at the station to the source of power thereat by connecting said one terminal of the light to the source when the communication direction control switch conditions the station for transmission, a pair of resistors connected across the loudspeaker at each station, and a connection from between said last mentioned resistors to said common ground, whereby when the communication direction control switches at either or both of two stations connected to an interstation circuit connect the stations for reception, both lights are grounded and when both connect the stations for transmission, both lights are ungrounded and lit.

14. In an intercommunicating system of the loudspeaker type including a station having a loudspeaker connected to an interstation circuit and utilizable both as a receiver and a microphone, and a second station of the type having a loudspeaker utilizable both as a receiver and a microphone, an amplifier, and a communication direction control switch normally connecting the loudspeaker to the interstation circuit and operable to connect said loudspeaker to the amplifier output or input and for simultaneously connecting the interstation circuit to the amplifier input or output, whereby the second mentioned station can control the direction of communication by operation 01 the communication direction control switch betweensaid two last mentioned positions,

the combination including, signal means at the second station, control means at the second station for conditioning said signal means for operation when the communication direction control switch connects the loudspeaker to the amplifier input and the amplifier output to the interstation circuit, and control means at the first station for operating said signal means when conditioned for operation, whereby the first station can signal the second station of a desire to break in on the transmission therefrom.

15. In an intercommunicating system of the loudspeaking type including a station having a loudspeaker connected to an interstation circuit and utilizable both as a receiver and a microphone, and a second station having a loudspeaker utilizable as a receiver or a microphone, an amplifier, a communication direction control switch normally connecting the loudspeaker to the interstation circuit and operable to connect the loudspeaker and the interstation circuit alternately to the output or input of the amplifier, and station selector switch means in the interstation circuit, the combination including, a pair of resistors connected across the interstation circuit intermediate the communication direction control switch and station selector means, a signal light, a source of power, a ground circuit, a circuit connecting one terminal of the light to the junction of said pair of resistors and the other terminal to said ground circuit, a second pair of resistors connected across the loudspeaker, a circuit connecting the junction of said second pair of resistors to said ground circuit, and switch means associated with the communication direction control switch for connecting said one terminal oi the light at the station to said source of power when said switch connects the loudspeaker to the amplifier input and the amplifier output to the interstation circuit, and control means at the second station normally grounding said one terminal oi. said light and operable to unground said one terminal.

16. In an intercommunicating system of the loudspeaker type including at least a pair of stations of the type having a loudspeaker utilizable both as a receiver and a microphone, an amplifier, and a communication direction control switch normally connecting the loudspeaker to an interstation circuit and operable to connect said loudspeaker to the amplifier output or input and for simultaneously connecting the interstation circuit to the amplifier input or output, whereby one station can control the direction of communication by operation of the communication direction control switch between said two last mentioned positions, the combination including, signal means at the stations, control means for conditioning said signal means at a station for operation when the communication control switch at the station connects the loudspeaker to the amplifier input and the amplifier output to the interstation circuit, and control means at the stations for operating said signal means when conditioned for operation, whereby stations can signal stations conditioned for transmission of a desire to break in on the transmission therefrom.

17. In an intercommunicating system of the loudspeaking type including a plurality of stations of the type having a loudspeaker utilizable as a receiver or a microphone, an amplifier, a

communication direction control switch normally connecting the loudspeaker to an interstation circuit and operable to connect the loudspeaker and an interstation circuit alternately to the output or input of the amplifier, and station selector switch means at each station in, the interstation circuit, the combination including, a pair of resistors connected across the interstation circuit intermediate the communication direction control switch and station selector means, a signal light, a source of power, a ground circuit, a circuit connecting one terminal of the light to the Junction of said pair of resistors and the other terminal to said ground circuit, a second pair of resistors connected across the loudspeaker, a circuit connecting the junction of said second pair of resistors to said ground circuit, and switch means associated with each communication direction control switch for connecting said one terminal of the light at the station to said source of power when said switch connects the loudspeaker to the amplifier input and the amplifier output to the interstation circuit.

18. In an intercommunicating system oi! the loudspeaker type including at least one station of the type having a loudspeaker utilizable both as a receiver and a microphone, an amplifier, and a communication direction control switch for alternately connecting said loudspeaker to the amplifier output and input and for simultaneously connecting an interstation circuit to the amplifier input and output, and at least one station of a type having a loudspeaker utilizable both as a receiver and a microphone connected to said interstation circuit, the combination including, signal means at the stations of the first type, control means for conditioning said signal means for operation when stations are conditioned for transmission, and control means at signal means when conditioned for operation, whereby stations or the second type can signal stations of the first type or a desire to break in on the transmission therefrom.

19. In an intercommunicating system of the loudspeaking type including a first station of the type having a loudspeaker utilizableas a receiver or a microphone, an amplifier and a communication direction control switch adapted to connect the loudspeaker and an interstation circuit alternately to the output and input of the amplifier, and a second station having a loudspeaker permanently connected to the interstation circuit, the combination including, a pair of resistors connected across the loudspeaker at the second station, a circuit including a normally closed switch at the second station connecting the junction of said resistors to ground, a second pair of resistors connected across the interstation circuit at the first station, a signal light, a source of power, a circuit connecting one terminal of the light to the junction of said second pair of resistors and the other terminal to said ground, a third pair of resistors connected across the loudspeaker at the first station, a circuit connecting the junction of said third pair of resistors to said ground, and switch means associated with said communication direction control switch for connecting said one terminal of said light to said source of power when said switch connects the loudspeaker to the amplifier input and the amplifier output to the interstation circuit.

RICHARD H. CAMPBELL.

7 stations of the second type for operating said 

